USB ports on a laptop are used to charge various electronic devices, such as cell phone and music players. Typically, the electrical power is cut-off to the USB port when the laptop goes to a sleep mode or shut down, such that the electronic devices cannot be charged through the USB ports.
FIG. 1 illustrates a typical charging module 100 including an adaptor 102 couples with a laptop 104. The adaptor 102 can output a voltage V1 in a battery 106 charging mode. During the charging mode, switch S1 108 is on “ON” or closed. A DC/DC converter 112 converts V1 from 12V˜20V to V2 (such as 5V). V2 can be used for one or more USB ports 114 through a switch S2 110. S2 110 can be controlled by a controller to protect USB port at over current, short circuit and other abnormal conditions. When the laptop 104 goes into a deep sleep mode or power off conditions (S1 108 and/or S2 110 is OFF), the USB ports 114 cannot be used.